/**
 * @param {number} n
 * @return {number}
 */
var climbStairs = function(n) {
  let dp = []
  dp.push(0, 1, 2)
  for (let i = 3; i <= n; i++) {
    dp[i] = dp[i-1] + dp[i-2]
  }
  return dp[n]
};

climbStairs(3)